The Fetch Sequence Dialog

The fetch sequence dialog box (see Figure 22) lists on the left side (under "Fetch Sequence Implementation") the current sequence of microinstructions forming the fetch sequence.

Figure 22. The fetch sequence dialog.

If you wish to delete one of the microinstructions from the sequence, delete it by dragging it out from the Fetch Sequence Implementation list. If you wish to insert a new microinstruction in the sequence, drag the microinstruction you want from the list in the right part of the dialog box into the implementation sequence. To reorder the microinstructions in the fetch sequence, just drag them up or down in the list.

In the list of all microinstructions on the right, there is a microinstruction named "Comment". When executed, this microinstruction does nothing. Instead, this microinstruction plays the role of a comment in the fetch sequence's implementation. To add a Comment micro to the fetch sequence, drag it into the implementation sequence. You can now edit the comment in the implementation list by double-clicking it (or pressing F2). Comments are colored gray to distinguish them from regular microinstructions. It is recommended that you start all comment micros with a special comment character to distinguish them from regular microinstructions.

Note: Every fetch sequence needs a Decode microinstruction in its implementation. The Decode microinstruction causes CPU Sim to decode the fetched instruction and begin executing the microinstructions in its execute sequence.